Many different methods and corresponding apparatus are known for mounting and for removing and replacing electronic components on printed circuit boards. A known reflow soldering system In the pin-in-hole technology area uses a stencil to deposit solder alloy paste containing a flux at attachment points at the holes in a printed circuit board. The water soluble or rosin flux is applied only to the solder side of the circuit card. The components are then placed in the holes at the solder paste deposits and heat and/or pressure is then applied to reflow the solder paste. Alternatively the solder is melted from underneath the board through the holes after application of flux, using a solder wave fountain. The flux residues are then removed from the assembled circuit board using a suitable solvent. The purpose of the flux material is to enable the solder to wet the connecting metallic surfaces of the printed circuit board and the electronic component. It also promotes heat flow between the component and circuit connection points and discourages air gaps which could result in a defective solder joint. This method is commonly used when first connecting components to printed circuit boards but is not practical for replacing single damaged or defective components from a populated printed circuit board.
Disadvantages of this type of soldering is that the flux based soldering paste results in unwanted resultant contaminants and other chemicals which can cause electrical shorting and other product failures. The build up of flux residue means that costly and time consuming cleaning operations are necessary. Many of these cleaning operations have proven to be environmentally unsound. Attempts to use the mini solder wave process with low solids no clean flux have resulted in a mass of solder tags and solder webbing. This is a particular problem when a component is being removed by melting the solder with a mini solder wave fountain. As the electronics industry is moving inexorably to a total no clean process, a solution to such repair processes is essential.
Another known method for removing electronic components includes directing a hot jet of gas (e.g., nitrogen) through a nozzle to the solder joints of the electronic component. A problem with this type of system is that the gas needs to be directed in a concentrated area to prevent heating up adjacent components and possible damage to the circuit board. Either multiple nozzles must be employed or the solitary nozzle repositioned for each solder joint to be reflowed. This method is also unsuitable for use with larger electronic components which have a high number of leads. It is difficult to reflow all the solder joints at the same time without damaging the component.
A known method which attempted to overcome the problems solved by using flux involved carrying out the reflow process within a large oven containing nitrogen gas to try and prevent the formation of metal oxides during reflow soldering. One problem with this approach was that the oven proved expensive to operate and the oxides were not entirely eliminated.
In U.S. Pat. No. 4,847,465 (Toyama et al.), there is shown a reflow soldering apparatus for reflowing solder to secure leaded (pinned) and other parts on a circuit board. This apparatus requires relatively complex heat pipe members which, as shown, project externally of the gas chamber housing. This adds cost as well as increases the opportunity for operator injury during apparatus operation. This patent also fails to address the opportunity for fluxless soldering, an important feature available in the present invention.
None of the known methods provides a method and apparatus which does not include expensive ovens of or the production of large amounts of flux residues which need to be cleaned from the printed circuit board. It is believed that such a method and apparatus would constitute an advancement in the art.